A parallel hybrid vehicle comprising a motor and an engine as sources of drive force, which runs under the drive force of either or both of the motor and engine, is disclosed on pp. 39-52 of "Automotive Engineering" Vol.46 No.7 June, 1997 published by the Tetsudo Nihon Sha.
This vehicle runs only under the drive force of the motor when the vehicle load is small, and the engine is operated to increase the drive force when the vehicle load exceeds a predetermined level.